BABAR Collaboration(Lees, J. P. et al), Azzolini, V., Martinez-Vidal, F., & Oyanguren, A. (2012). Study of (B)over-bar -> X(u)l(v)over-bar decays in B(B)over-bar events tagged by a fully reconstructed B-meson decay and determination of vertical bar V-ub vertical bar. Phys. Rev. D, 86(3), 032004–23pp.
Abstract: We report measurements of partial branching fractions for inclusive charmless semileptonic B decays (B) over bar -> X(u)l (v) over bar and the determination of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element vertical bar V-ub vertical bar. The analysis is based on a sample of 467 x 10(6) Y(4S) -> B (B) over bar decays recorded with the BABAR detector at the PEP- II e(+)e(-) storage rings. We select events in which the decay of one of the B mesons is fully reconstructed and an electron or a muon signals the semileptonic decay of the other B meson. We measure partial branching fractions Delta B in several restricted regions of phase space and determine the CKM element vertical bar V-ub vertical bar based on different QCD predictions. For decays with a charged lepton momentum p(l)* > 1.0 GeV in the B meson rest frame, we obtain Delta B = (1.80 +/- 0.13(stat) +/- 0.15(sys) +/- 0.02(theo)) x 10(-3) from a fit to the two-dimensional M-X – q(2) distribution. Here, M-X refers to the invariant mass of the final state hadron X and q(2) is the invariant mass squared of the charged lepton and neutrino. From this measurement we extract vertical bar V-ub vertical bar = (4.33 +/- 0.24(exp) +/- 0.15(theo)) x 10(-3) as the arithmetic average of four results obtained from four different QCD predictions of the partial rate. We separately determine partial branching fractions for (B) over bar (0) and B- decays and derive a limit on the isospin breaking in (B) over bar -> X(u)l (v) over bar decays.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2013). Branching fraction measurement of B+ -> omega l(+)nu decays. Phys. Rev. D, 87(3), 032004–11pp.
Abstract: We present a measurement of the B+ -> omega l(+)nu branching fraction based on a sample of 467 million B (B) over bar pairs recorded by the BABAR detector at the SLAC PEP-II e(+)e(-) collider. We observe 1125 +/- 131 signal decays, corresponding to a branching fraction of B(B+ -> omega l(+)nu) = (1.21 +/- 0.14 +/- 0.08) x 10(-4), where the first error is statistical and the second is systematic. The dependence of the decay rate on q(2), the invariant mass squared of the leptons, is compared to QCD predictions of the form factors based on a quark model and light-cone sum rules.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2012). Search for the decay modes D-0 -> e(+) e(-), D-0 -> mu(+) mu(-), and D-0 -> e(+/-) μ-/+. Phys. Rev. D, 86(3), 032001–10pp.
Abstract: We present searches for the rare decay modes D-0 -> e(+) e(-), D-0 -> mu(+) mu(-), and D-0 -> e(+/-) mu(-/+) in continuum e(+) e(-) -> c (c) over bar events recorded by the BABAR detector in a data sample that corresponds to an integrated luminosity of 468 fb(-1). These decays are highly Glashow-Iliopoulos-Maiani suppressed but may be enhanced in several extensions of the standard model. Our observed event yields are consistent with the expected backgrounds. An excess is seen in the D-0 -> mu(+) mu(-) channel, although the observed yield is consistent with an upward background fluctuation at the 5% level. Using the Feldman-Cousins method, we set the following 90% confidence level intervals on the branching fractions: B(D-0 -> e(+) e(-)) < 1.7 x 10(-7), B(D-0 -> mu(+) mu(-)) within [0.6,8.1] x 10(-7), and B(D-0 -> e(+/-) mu(-/+)) < 3.3 x 10(-7).
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2016). Search for mixing-induced CP violation using partial reconstruction of (B)over-bar(0) -> D*(+)Xl(-)(nu)over-bar(l) and kaon tagging. Phys. Rev. D, 93(3), 032001–13pp.
Abstract: We describe in detail a previously published measurement of CP violation in B-0-(B) over bar (0) oscillations, based on an integrated luminosity of 425.7 fb(-1) collected by the BABAR experiment at the PEPII collider. We apply a novel technique to a sample of about 6 million (B) over bar (0) -> D*(+)l(-)(nu) over bar (l) decays selected with partial reconstruction of the D*(+) meson. The charged lepton identifies the flavor of one B meson at its decay time, the flavor of the other B is determined by kaon tagging. We determine a CP violating asymmetry A(CP) = (N((BB0)-B-0) – N((B) over bar (0)(B) over bar (0)))/(N((BB0)-B-0) + N((B) over bar (0)(B) over bar (0))) = (0.06 +/- 0.17(-0.32)(+0.38))% corresponding to Delta(CP) = 1-vertical bar q/p vertical bar = (0.29 +/- 0.84(-1.61)(+1.88)) x 10(-3). This measurement is consistent and competitive with those obtained at the B factories with dilepton events.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2017). Search for B+ -> K+tau(+)tau(-) at the BABAR Experiment. Phys. Rev. Lett., 118(3), 031802–8pp.
Abstract: We search for the rare flavor-changing neutral current process B+ -> K+tau(+)tau(-) using data from the BABAR experiment. The data sample, collected at the center-of-mass energy of the Upsilon(4S) resonance, corresponds to a total integrated luminosity of 424 fb(-1) and to 471 x 10(6) B (B) over bar pairs. We reconstruct one B meson, produced in the Upsilon(4S) -> B+B- decay, in one of many hadronic decay modes and search for activity compatible with a B+ -> K+tau(+)tau(-) decay in the rest of the event. Each tau lepton is required to decay leptonically into an electron or muon and neutrinos. Comparing the expected number of background events with the data sample after applying the selection criteria, we do not find evidence for a signal. The resulting upper limit, at the 90% confidence level, is B(B+ -> K+tau(+)tau(-)) < 2.25 x 10(-3).
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